In general, the locations of internal tumors are obtained using CAT or MRI scans. However, these tumors within the body cavity may move due to motion of the patient (gravity pressure) or due to gastrointestinal pressures. It is essential to limit the treatment irradiation to the tumor site, and prevent irradiation of nearby healthy tissue. This is especially true for some organs, e.g. a liver, which may lie next to organs such as ovaries which are highly sensitive to radiation
A method of locating an internal injury is disclosed in U.S. Pat. No. 5,755,746 issued on May 26, 1998 to Arthur Lifshey et al. This approach involves positioning, at an external location that is approximately adjacent to the internal injury, a marker that is visualizable by X-rays, magnetic resonance, or ultrasonic waves. This approach appears to lack accuracy for tumors and other internal structures because the marker is external (and thus distant) from the internal injury, and because internal structures are likely to move within the body.